This routine is designed to convert the SMAP L2 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture, Soil moisture product (Versions 4-8) to a DART observation sequence file.
Quoting the NSIDC:
This Level-2 (L2) soil moisture product provides estimates of global land surface conditions retrieved by the Soil Moisture Active Passive (SMAP) passive microwave radiometer during 6:00 a.m. descending and 6:00 p.m. ascending half-orbit passes. SMAP L-band brightness temperatures are used to derive soil moisture data, which are then resampled to an Earth-fixed, global, cylindrical 36 km Equal-Area Scalable Earth Grid, Version 2.0 (EASE-Grid 2.0).
Data Set ID: SPL2SMP SMAP L2 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture
Surface soil moisture (0-5 cm) in m3/m3 derived from brightness temperatures (TBs) is output on a fixed global 36 km EASE-Grid 2.0. Also included are brightness temperatures in kelvin representing the weighted average of Level-1B brightness temperatures whose boresights fall within a 36 km EASE-Grid 2.0 cell.
Important
SMAP_L2_to_obs
uses an
observation error standard deviation of 0.01 m3/m3 or 20% of the soil moisture
value, whatever is higher. These numbers have no scientific basis and
should be thoroughly explored. The data files I have explored have
a variable soil_moisture_error but these appear to be
empty - i.e. full of _FillValue values. A better way
of specifying the observation error standard deviation is needed.
Important
SMAP_L2_to_obs has only been thoroughly tested with the half-orbit files - these files have names like 'SMAP_L2_SM_P_02526_D_20150723T070211_R12170_001.h5'.
Important
SMAP_L2_to_obs is not compatible with SMAP L3 files as they are formatted differently
The workflow is usually:
- Download the data for the period in question (see DATA SOURCES below)
- Build the DART executables with support for the soil moisture observations. This is done by running preprocess with
obs_def_land_mod.f90
in the list of input_files forpreprocess_nml
.- Convert each data file individually using
SMAP_L2_to_obs
- Combine or subset all output files for the region and timeframe of interest into one file using :doc:`../../../assimilation_code/programs/obs_sequence_tool/obs_sequence_tool`
For some models (CLM, for example), it is required to reorganize the observation sequence files into a series of files that contains ONLY the observations for each assimilation. This can be achieved with the ~/models/clm/shell_scripts/makedaily.sh script. Since there are subtleties for each model, makedaily.sh is generally found in the shell_scripts directory of the model.
This namelist is read from the file input.nml. Namelists start with an ampersand '&' and terminate with a slash '/'. Character strings that contain a '/' must be enclosed in quotes to prevent them from prematurely terminating the namelist.
&SMAP_L2_to_obs_nml input_file_list = 'file_list.txt' obs_out_file = 'obs_seq.out' max_num_input_files = 10 verbose = .false. /
Description of namelist variables:
Contents | Type | Description |
---|---|---|
input_file_list | character(len=256) | Name of the file containing the list of input data files. Each input data file name must be on a separate line. No blank lines are allowed. This may be a relative or absolute filename. |
obs_out_file | character(len=256) | Name of the output observation sequence file. |
max_num_input_files | integer | The maximum number of filenames in 'input_file_list' to convert. This should be a small number - converting all frequencies, all polarizations, both passes into one file is not recommended |
verbose | logical | Print extra information during the SMAP_L2_to_obs execution. |
The SMAP L2 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture, Version 4 data
The following example shows how to cite the use of this data set in a publication. For more information, see the Use and Copyright web page
O'Neill, P. E., S. Chan, E. G. Njoku, T. Jackson, and R. Bindlish. 2016. SMAP L2 Radiometer Half-Orbit 36 km EASE-Grid Soil Moisture, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/XPJTJT812XFY. [Date Accessed].
The SMAP_L2_to_obs.f90
file is the source
for the converter program.
To compile and test,
go into the work subdirectory and run the quickbuild.sh
script to build the converter and a couple of general purpose utilities.
:doc:`../../../assimilation_code/programs/advance_time/advance_time`
helps with calendar and time computations, and the
:doc:`../../../assimilation_code/programs/obs_sequence_tool/obs_sequence_tool`
manipulates DART observation files once they have been created.
See the discussion in the :doc:`../../../guide/creating-obs-seq-real/` introduction page about what options are available for the things you need to specify. These include setting a time, specifying an expected error, setting a location, and an observation type.
DART software - Copyright UCAR. This open source software is provided by UCAR, "as is", without charge, subject to all terms of use at http://www.image.ucar.edu/DAReS/DART/DART_download